This disclosure is directed to a shock activated switch which is capable of providing electrical circuit switching. The switch is adapted to be installed in a downhole perforating gun assembly which supports a number of perforating guns. The perforating gun assembly supports a plurality of shaped charges which are used to form perforations into the surrounding pipe, which defines the well, the cement on the exterior and into adjacent formations to produce from productive formations. The perforating gun assembly normally incorporates a number of such shaped charges and they are collectively fired by additional explosives in the perforating gun assembly. A significant shock wave is formed in the confines of the well borehole, the shock wave propagating up the borehole. The shock wave may substantially destroy the operating equipment that is included in the perforating gun assembly. It is particularly important to have equipment in the perforating gun assembly which is able to withstand this shock wave. It is important so that signals can be conveyed from the perforating gun assembly back to the well surface so that the operator knows the operative state of the equipment. One important signal which is required is the signal that firing has actually occurred.
The present apparatus is directed to a pressure responsive switch. It is exposed to the shock wave created by the explosion of the shaped charge in the well borehole. Moreover, the switch is intentionally exposed to this high pressure shock wave so that surface personnel and provided with switch initiated signals to identify the actual moment or instant of firing. This is therefore a rugged, difficult environment in which to expect a pressure operated switch to operate properly. The present apparatus provides such safe operation and is particularly able to transmit the requisite electrical signal notwithstanding the fact that the switch itself may be destroyed by the shock wave originating in the narrow confines at the location of the perforating gun assembly.
The present apparatus is surprisingly and particularly simple in construction so that it has only a single moving assembly. This moving assembly can be treated as a sacrificial member. In other words, it is not necessary to be used again and again. Rather, it may be destroyed in the violence of the explosion, but it will, even in its own destruction, provide the necessary signal through electrical conductors connected to the surface which indicates that the firing has actually occurred. This therefore is a highly reliable switch which forms the electrical signals of interest. The present apparatus includes a movable switch element which will be described as the piston operated, stem mounted actuator. It is cooperative with a sleeve which is positioned in the perforating gun assembly having a countersunk and undercut hole therein. The sleeve is fixed in location. It is constructed so that it can make one circuit on movement and break another circuit at the same instant. In this arrangement, the event of interest (detonation of explosives) can be signaled either by the make or break which occur on actuation.